The present invention relates to an inline electron gun assembly for a plural beam cathode-ray tube (CRT) and, more particularly, to a structure for strengthening the sidewall of a cup-shaped member of such a gun assembly.
The electrode members of an inline electron gun assembly are serially arranged to accelerate and focus a plurality of electron beams along spaced, co-planar electron beam paths. The electrode members of the gun assembly are mechanically secured by means of attachment tabs and studs to at least a pair of insulative support rods which extend along the beam paths. Each of the electrode members commonly has several spatially-related apertures formed therein to accommodate the respective electron beams generated within the electron gun assembly. It is important that these several apertures be accurately located and aligned relative to the related apertures in adjacent electrode members, and to the respective electron generating surfaces. During the fabrication of the electron gun assembly, the attachment tabs and studs of the various electrode members are embedded into the temporarily heat-softened insulative support rods at which time the support rods on opposed sides of the gun assembly are pressured inwardly toward the electrode members to force the attachment tabs and studs into the support rods. The compressive pressure tends to exert a distorting force upon the several deep-drawn, cup-shaped electrode members which comprise the main focus lens of the electron gun assembly.
Most experience to date with conventional deep-drawn, cup-shaped electrodes, having sidewalls up to about 12.7 mm long, shows that these electrodes tend to develop a negative or concave "oil-canning" tendency, i.e., the sidewall of the electrode tends to bow inwardly toward the electron beam axes. When studs are welded to opposite sides of the sidewall of such electrodes, exact positioning and welding are difficult because of the variable slope and degree of negative "oil-canning" that occurs.
An even greater problem has been encountered in electron guns in which ultra-deep drawn, cup-shaped electrodes have sidewalls more than 12.7 mm long. In such ultra-deep drawn electrodes, a critical thinning of the sidewall occurs. The apex of the "oil-canning" in these electrodes occurs about 10.16 mm from the support flange located at the open end of the electrode. In the vicinity of the apex, the sidewall thins from the desired thickness of about 0.25 mm to about 0.19 mm. If the "oil-canning" is negative or concave on both sides of the sidewall, the problem of stud positioning is similar to that of the shorter deep-drawn electrodes described above; however, if the "oil-canning" of one side of the sidewall is positive or convex and the other side is negative or concave, or if both sides exhibit positive or convex "oil-canning," a new phenomenon occurs. During the beading operation, in which the insulative support rods are heated to a molten state and formed into contact with the attachment tabs and studs of the electron gun, the positive or convex "oil-canning" sidewall is forced inward by the stud attached to the sidewall of the previously convex surface.
The inward displacement of the previously convex sidewall acts like a loaded spring. As soon as the arms of the beading apparatus retract at the end of the beading cycle, the compressed sidewall of the electrode tends to return to its previous convex position forcing the insulative support rods, which are still in a plastic state, to bulge outwardly. Shear forces are thereby introduced into the insulative support rods during the cooling-deflection cycle, causing the support rods to crack in the vicinity of the attachment tabs or studs.
Even in electron guns in which the stress forces are not sufficiently great to crack the support rods, the varying degree of "oil-canning" of the sidewalls can cause a side-to-side displacement or offset of the ultra-deep drawn electrode relative to the other electrode members of the main focus lens. This results in a change of aperture locations relative to those in the adjacent electrode members, thereby producing deleterious inter-electrode spacing relationships and distortion in the electron beam trajectories.
U.S. Pat. No. 4,484,102, issued to J. R. Hale on Nov. 20, 1984, discloses a structure for strengthening the sidewall of a conventional deep-drawn electrode. The structure described therein comprises a wedge-shaped shoulder that is formed in opposite parallel sides of the sidewall of a deep-drawn substantially rectangular cup-shaped member. The wedge-shaped shoulder projects outwardly at an acute angle of about 45 degrees from the sidewall and extends into the supporting flange of the electrode adjacent to the attachment tabs. This structure is insufficient to prevent flexure of the sidewall of ultra-deep drawn electrodes.
U.S. Pat. No. 4,595,858, issued to J. R. Hale on Jun. 17, 1986, discloses a structure suitable for reinforcing either deep-drawn or ultra-deep drawn electrodes. A pair of reinforcing ribs are formed into each of the opposed parallel sides of the sidewall of the electrode to minimize flexure of the opposed sides in the vicinity of the studs, which are attached to the sidewall and embedded into the glass support rods, so as to minimize deleterious displacement, i.e., "oil-canning" of the electrode. However, the reinforcing ribs formed in the sidewall do nothing to provide a flat welding surface for the studs. Accordingly, a structure is desired which simultaneously strengthens the sidewall of the electrode while providing a flat surface for attachment of the studs.